It is proposed to study the kinetics of the oxygen isotope exchange reaction that occurs between water and formic acid in liquid solution. This reaction provides a model for the study of hydrolysis, acid catalysis, and the general behavior of protons and water molecules in concentrated aqueous solution. It serves as a prototype for the hydrolysis steps that occur in many reactions of complex biological systems, including enzymatic hydrolysis reactions. It will be studied over a range of reagent concentrations, temperatures, and pH values. Emphasis will be on very concentrated formic acid solutions (e.g. with mole fractions up to 0.5). The numerous formic acid isotopic congeners are easy to handle experimentally, are likely to show large kinetic isotope effects, and the molecule is small enough to be tractable theoretically. Rate constants for twelve distinct isotopic congeners ivnolving D, 13C and 18O substitutions of the HCOO skeleton will be investigated and these are multiplied by deuteration or partial deuteration of the hydroxyl/water system. If all the feasible heavy atom kinetic isotope effects are resolved they will contribute to a far more extensive KIE data base than is presently available for the investigation of any chemical reaction mechanism. This data base is fundamental because kinetic isotope effects provide experimental probes for studying properties of reaction transition states. The research is also intended to test the general suitability of using matrix-isolation infrared spectroscopy as the analytical method for this type of study. This is a novel application of matrix-isolation sampling, and spectroscopy is very advantageous for isotopic studies if questions exist concerning the atomic position of the isotopic label. Success with the present problem will invite application of the method to other reaction systems.